Hi Fraser, thanks a lot for your quick response.
If I don’t throttle my connection quite heavily, I can barely get decent results — I’ve tested quite a bit. I’ve now placed my Netduma R3 in the DMZ. In addition, I just installed firmware version v4.0.645. There’s also an option from my ISP to get the Fritzbox 6660 modem but unfortunately, it can’t be put into bridge mode either. What else can I do to improve things?